1. Field of the Invention
The present invention relates to radio direction finding antennas, and particularly to a circular antenna array for vehicular direction finding.
2. Description of the Related Art
Wireless technology, such as radio frequency (RF) and direction finding (DF) systems, have been popular with the military since their first use in World War II. Traditionally these systems were used in war zones to detect the presence of unwanted transmitters, a term commonly referred to in the military as “fox hunting”. This process involved rotating a directional antenna across the 360° azimuth plane to find the most probable direction of unwanted transmission. If the “fox” transmitted for long enough, its position could be located quite accurately. More recently, direction finding has been utilized in civilian applications including disaster recovery, wildlife tracking and locating illegal transmitters in licensed frequency bands. One emerging application of direction finding is to locate a car in a huge parking lot; utilizing antenna beam scanning and transmission of beacon signals.
The majority of the initial direction finding antenna systems used multiple channel receiver systems, where every antenna element on the array had a corresponding receiver. These systems were bulky and consumed too much power, and in some cases, were impractical due to mobility related issues. Recent advances in integrated chip (IC) and digital signal processing (DSP) technologies have given rise to small, portable and highly versatile single-channel DF systems. In order to accurately determine the position of the object in the far-field of the antenna, it is desired to have a high gain (in the desired plane) and extremely narrow half-power beamwidths (HPBW). Moreover, the scanning angle can be increased by modifying the geometry of the antenna array. Linear antenna arrays have a maximum scan angle of 180°, but as the array becomes two-dimensional (by adding elements in both planes), the scan angle can be increased to 360°. Circular antenna arrays are an example of antenna arrays with a 360° scan angle. The selection of the antenna elements constituting the array is made on the basis of the individual radiation characteristics of the respective element types.
As mentioned above, it is desirable for antenna elements to have narrow HPBW and high gains for high accuracy. Several antenna array designs exist, but none appear to have actually been designed specifically for direction finding with vehicle localization as its application.
Thus, a circular antenna array for vehicular direction finding solving the aforementioned problems is desired.